1. Field of the Invention
This invention relates to an electronic apparatus which includes a photoelectric switch.
2. Description of the Related Art
As shown for example in FIGS. 28 and 29, which are longitudinal sectional views as seen from different directions, a photoelectric switch includes a case 101 having an opening, an element holder 104 mounted at the opening and having an infrared light-emitting diode 102 and a phototransistor 103, and lenses 105 provided on respective optic axes. The case opening is closed by the lenses 105. A plate 106 is provided on the upper portion of the case 101, and light-emitting diodes 107, 108 for display purposes are provided on a predetermined portion of the plate. Also provided on the plate are dials or the like for sensitivity adjustment. The photoelectric switch also includes a terminal base portion 109, which is for switching on and off an externally applied signal, provided below a printed circuit board 112. A cable is inserted from an opening 110 provided in the back side of the case and is fixedly connected to a terminal on the terminal base portion 109.
With a photoelectric switch of this kind, the terminal base portion 109 provided with the terminal to which the cable is connected is situated at the lower part of the photoelectric switch. Consequently, after the printed circuit board 112 has been mounted on the upper portion, it is difficult to attach and detach the terminus of the cable and labor is required for wiring and maintenance operations. Further, a sealing structure between the lenses and a frame is achieved by providing an O-ring between a cover and the case, which has an L-shaped cross section, by way of example. However, a sufficiently air-tight and water-proof structure cannot be obtained owing to gaps between the lenses and frame and movement of the cover. Though use is also made of a photoelectric switch in which the frame is provided inside the case, the element holder and the frame are not designed as a unitary body. Consequently, more labor is needed for mounting and the molds needed are more complicated. The end result is higher manufacturing cost.
Furthermore, with a photoelectric switch of this type, the connecting portion between the terminal base and the printed circuit board is not so designed that the pin of a terminal attaching piece 111 is introduced into the printed circuit board 112. Accordingly, the terminal attaching piece 111 and the printed circuit board 112 are connected at a position indicated by a soldered portion 113. As a consequence, inserting the terminal attaching piece into the printed circuit board and soldering them together is difficult and results in poor assembly operability. In addition, there is little tensile strength in the direction of the arrow and automatic assembly is not possible.
In photoelectric switches and the like, a frame is provided within a case in order to fix a variety of parts. A printed circuit board is attached to the frame. In a case where a display lamp such as a light-emitting diode is attached to the printed circuit board, as shown in the top view of FIG. 30 and sectional view of FIG. 31, an opening 122 is formed in a frame 121, holes are provided in a printed circuit board 123 at a position corresponding to the opening 122, a display element 124 is inserted from above into the opening 122 of the frame 121 and into terminal holes of the printed circuit board 123, and the display element is attached by being soldered from below.
In an electronic apparatus of this kind, the fact that the display element 124 is inserted from the opening 122 at the upper side of the frame 121 makes it difficult to insert the terminals of the display lamp into the holes of the printed circuit board 123. In addition, assembly operability is poor since the soldering operation is performed by hand. Furthermore, a great deal of labor is involved and automatic assembly is not feasible.
In another photoelectric switch, as shown for example in the sectional view of FIG. 32, a holding portion 132 of a photoelectric element 131 to which are attached a light-emitting element and a light-receiving element is provided inside a case 130. There are cases in which a filter 133 such as a color filter or polarizing filter is attached to a horn-shaped part of the photoelectric element holding portion 132. When the filter is attached in the photoelectric switch of this type, the filter 133 is inserted into a portion cut away into a rectangular shape to conform to the shape of the filter 133, as shown in FIG. 33 which is a front view of the photoelectric element holding portion 132, and the horn-shaped portion surrounding the filter is deformed as by a soldering iron to secure the filter 133. Further, as shown in FIG. 34, the photoelectric element holding portion is provided with bosses 134, 135, the filter 133 is inserted into the rectangularly shaped cut-out portion of the horn-shaped holding member 132 with openings in the filter 133 being registered with the bosses 134, 135, and the bosses 134, 135 are deformed by heat to fix the filter 133.
However, in a photoelectric switch having such a filter, it is necessary to attach the filter at a position deep within the horn-shaped part of the photoelectric element holding portion. As a result, not only is an operation such as heat-caulking difficult to perform and greater labor required, but the filter may be damaged and cannot be secured normally. This tends to result in defective articles.
Photoelectric switches are classified into three types, names a transmission type, diffuse reflection type and regressive reflection type. In the reflection-type photoelectric switches, it is necessary to provide a light-emitting element and a light-receiving element at the front side of the case. Since the transmission-type photoelectric switch has a configuration in which the light-emitting element and light-receiving element are separated, only one of these is disposed on the front side of the switch. In order to converge the light beams from these photoelectric elements on a predetermined area or condense the reflected light beams, a lens is provided on the front side of the case. Each switch has its own special case depending upon switch type, and the arrangement is such that the lens is attached to the front side of the case and the light-emitting and/or light-receiving elements are secured within the case.
In accordance with a photoelectric switch of this kind, a different case is required for each kind of photoelectric switch. As a result, there are a large variety of parts and a great number of molds involved. This not only raises price but also complicates maintenance. If the transmission type photoelectric switch is adapted to use the same case as the reflection-type photoelectric switches in order that common cases can be employed, the lens will be offset far from the center of the photoelectric switch. This is undesirable in that it detracts from the appearance of the switch and therefore diminishes its commercial value.
In the photoelectric switch shown in FIGS. 28 and 29, no cover is provided for covering the terminals on the terminal base within the case. Accordingly, in cases where a commercial AC power supply is directly connected at the time of connection or adjustment, there is the danger of electric shock.
In order to protect the elements and circuitry mounted on the printed circuit board against electromagnetic noise, a shielding plate is attached to the printed circuit board of the electronic apparatus. In such case, projections 142 are provided on the bottom side of a box-shaped shielding plate 141, as shown in FIGS. 35 and 36, a printed circuit board 143 is provided with openings 143a at positions corresponding to these projections, the projections 142 are inserted into the corresponding openings 143a and the tips thereof are bent to secure the shielding plate 141, after which the projections 142 are connected by solder or the like to a grounded wiring pattern on the printed circuit board 143. The shielding plate 141 is thus attached to the printed circuit board 143.
In an electronic apparatus of this kind, it is necessary to insert the projections into the openings in the printed cirCuit board and bend the projections when attaching the shielding plate. This is a drawback in that labor is required at the time of assembly.
Furthermore, when an individual part 152 such as a light-emitting diode is attached to a printed circuit board 144, as shown in FIG. 37, the individual part 152 is retained in a holding portion 153 and an electrode pin 152a of the part is bent beforehand. The pin 152a is registered with and inserted into an opening 145 provided in the printed circuit board 144 and the pin is electrically connected and secured by soldering to a wiring pattern on the printed circuit board 144.
When the individual part is attached in this conventional arrangement, however, it is difficult to make the bend angle of the electrode pin 152a uniform, so that disparities in the bend angle usually occur. As a result, the electrode pin cannot be readily inserted into the opening 145 of the printed circuit board 144. In particular, when the assembly of the electronic apparatus is performed automatically, the electrode pin cannot be inserted into the opening of the printed circuit board unless the pin is bent appropriately. As a consequence, automation is difficult to achieve and assembly operability is poor when assembly is performed by hand.